The proposed research program aims to (1) define the immunochemical parameters underlying the development of erythroblastosis, and (2) design new quantitative prenatal tests with which to estimate accurately the severity of anticipated disease. Results of these proposed studies will be particularly important for (1) the assay of IgG antibodies to be used for the prevention of primary maternal immunization, and (2) clarification of immune mechanisms responsible for transfusion reaction and hemolytic anemia associated with autologous antibodies.